This invention relates to new chemical compounds, processes for their preparation, pharmaceutical formulations containing them and their use in therapy.
Inflammation is a primary response to tissue injury or microbial invasion and is characterised by leukocyte adhesion to the endothelium, diapedesis and activation within the tissue. Leukocyte activation can result in the generation of toxic oxygen species (such as superoxide anion), and the release of granule products (such as peroxidases and proteases). Circulating leukocytes include neutrophils, eosinophils, basophils, monocytes and lymphocytes. Different forms of inflammation involve different types of infiltrating leukocytes, the particular profile being regulated by the profile of adhesion molecule, cytokine and chemotactic factor expression within the tissue.
The primary function of leukocytes is to defend the host from invading organisms such as bacteria and parasites. Once a tissue is injured or infected a series of events occurs which causes the local recruitment of leukocytes from the circulation into the affected tissue. Leukocyte recruitment is controlled to allow for the orderly destruction and phagocytosis of foreign or dead cells, followed by tissue repair and resolution of the inflammatory infiltrate. However in chronic inflammatory states, recruitment is often inappropriate, resolution is not adequately controlled and the inflammatory reaction causes tissue destruction.
There is evidence from both in vitro and in vivo studies to suggest that compounds active at the adenosine A2a receptor will have anti-inflammatory actions. The area has been reviewed by Cronstein (1994). Studies on isolated neutrophils show an A2 receptor-mediated inhibition of superoxide generation, degranulation, aggregation and adherence (Cronstein et al, 1983 and 1985; Burkey and Webster, 1993; Richter, 1992; Skubitz et al, 1988. When agents selective for the A2a receptor over the A2b receptor (eg CGS21680) have been used, the profile of inhibition appears consistent with an action on the A2a receptor subtype (Dianzani et al, 1994). Adenosine agonists may also downregulate other classes of leucocytes (Elliot and Leonard, 1989; Peachell et al, 1989). Studies on whole animals have shown the anti-inflammatory effects of methotrexate to be mediated through adenosine and A2 receptor activation (Asako et al, 1993; Cronstein et al, 1993 and 1994). Adenosine itself, and compounds that raise circulating levels of adenosine also show anti-inflammatory effects in vivo (Green et al, 1991; Rosengren et al, 1995). In addition raised levels of circulating adenosine in man (as a result of adenosine deaminase deficiency) results in immunosuppression (Hirschorn, 1993).
Certain substituted 4xe2x80x2-carboxamido and 4xe2x80x2-thioamido adenosine derivatives which are useful for the treatment of inflammatory diseases are described in international Patent Application Nos. WO94/17090, WO96/02553, WO96/02543 (Glaxo Group). Substituted 4xe2x80x2-carboxamidoadenosine derivatives useful in the treatment of dementia are described in AU 8771946 (Hoechst Japan). Substituted 4xe2x80x2-hydroxymethyl adenosine derivatives which are useful for the treatment of gastrointestinal motility disorders are described in EP-A-423776 and EP-A-423777 (Searle). Substituted 4xe2x80x2-hydroxymethyl adenosine derivatives which are useful as platelet aggregation inhibitors are described in BE-768925 (Takeda). 4xe2x80x2-Hydroxymethyl adenosine derivatives and 4xe2x80x2-esters thereof which are useful as anti-hypertensive agents or have other cardiovascular activity are described in U.S. Pat. No. 4,663,313, EP 139358 and U.S. Pat. No. 4,767,747 (Warner Lambert), U.S. Pat. No. 4,985,409 (Nippon Zoki) and U.S. Pat. No. 5,043,325 (Whitby Research). 4-Hydroxymethyladenosine derivatives useful in the treatment of autoimmune disorders are described in U.S. Pat. No. 5,106,837 (Scripps Research Institute). 4xe2x80x2-Hydroxymethyladenosine derivatives useful as anti-allergic agents are described in U.S. Pat. No. 4,704,381 (Boehringer Mannheim). Certain 4xe2x80x2-tetrazolylalkyl adenosine derivatives which are useful in the treatment of heart and circulatory disorders are generically described in DT-A-2621470 (Pharma-Waldhof). Other 4xe2x80x2-carboxamidoadenosine derivatives useful in the treatment of cardiovascular conditions are described in U.S. Pat. No. 5,219,840, GB 2203149 and GB 2199036 (Sandoz), WO94102497 (US Dept. Health), U.S. Pat. No. 4,968,697 and EP 277917 (Ciba Geigy), U.S. Pat. No. 5,424,297 (Univ. Virginia) and EP 232813 (Warner Lambert). Other 4xe2x80x2-carboxamidoadenosine derivatives lacking substitution on the purine ring in the 2-position are described in DT 2317770, DT 2213180, U.S. Pat. Nos. 4,167,565, 3,864,483 and 3,966,917 (Abbott Labs), DT 2034785 (Boehringer Mannheim), JP 58174322 and JP 58167599 (Tanabe Seiyaku), WO92/05177 and U.S. Pat. No. 5,364,862 (Rhone Poulenc Rorer), EP 66918 (Procter and Gamble), WO86/00310 (Nelson), EP 222330, U.S. Pat. No. 4,962,194, WO88/03147 and WO88/03148 (Warner Lambert) and U.S. Pat. No. 5,219,839, WO95/18817 and WO93/14102 (Lab UPSA). 4xe2x80x2-Hydroxymethyladenosine derivatives lacking substitution on the purine ring in the 2-position are described in WO95/11904 (Univ Florida). 4xe2x80x2-Substituted adenosine derivatives useful as adenosine kinase inhibitors are described in WO94/18215 (Gensia). Other 4xe2x80x2-halomethyl, methyl, thioalkylmethyl or alkoxymethyl adenosine derivatives are described in EP 161128 and EP 181129 (Warner Lambert) and U.S. Pat. No. 3,983,104 (Schering). Other 4xe2x80x2-carboxamidoadenosine derivatives are described in U.S. Pat. No. 7,577,528 (NIH), WO91/13082 (Whitby Research) and WO95/02604 (US Dept Health).
Certain tetrazole containing deoxynucleotides which were found to lack anti-infective activity are described in Baker et al (1974) Tetrahedron 30, 2939-2942. Other tetrazole containing adenosine derivatives which show activity as platelet aggregation inhibitors are described in Mester and Mester (1972) Pathologie-Biologie, 20 (Suppl) 11-14. Certain nitrile containing ribose derivatives are described in Schmidt et al (1974) Liebigs. Ann. Chem. 1856-1863.
Other publications include: WO 98/16539 (Novo Nordisk A/S) which describes adenosine derivatives for the treatment of myocardial and cerebral ischaemia and epilepsy; WO 98/01426 (Rhone-Poulenc Rorer Pharmaceuticals Inc.) which relates to adenosine derivatives possessing antihypertensive, cardioprotective, anti-ischaemic and antilipolytic properties; and WO 98/01459 (Novo Nordisk A/S) which describes N,9-disubstituted adenine derivatives which are substituted in the 4xe2x80x2 position by unsubstituted oxazolyl or isoxazolyl and the use of such compounds for the treatment of disorders involving cytokines in humans. WO 98/28319 (Glaxo Group Limited) was published subsequent to the earliest priority date of this application and describes 4xe2x80x2-substituted tetrazole 2-(purin-9-yl)-tetrahydrofuran-3,4-diol derivatives.
We have now found a novel group of compounds with broad anti-inflammatory properties which inhibit leukocyte recruitment and activation and which are agonists of the adenosine 2a receptor. The compounds are therefore of potential therapeutic benefit in providing protection from leukocyte-induced tissue damage in diseases where leukocytes are implicated at the site of inflammation. The compounds of the invention may also represent a safer alternative to corticosteroids in the treatment of inflammatory diseases, whose uses may be limited by their side-effect profiles.
More particularly, the compounds of this invention may show an improved profile over known A2a-selective agonists in that they generally lack significant agonist activity at the human A3 receptor. This profile can be considered of benefit as A3 receptors are also found on leucocytes (eg eosinophil) and other inflammatory cells (eg mast cell) and activation of these receptors may have pro-inflammatory effects (Kohno et al, 1996; Van Schaick et al 1996). It is even considered that the bronchoconstrictor effects of adenosine in asthmatics may be mediated via the adenosine A3 receptor (Kohno et al, 1996).
Thus, according to the invention we provide compounds of formula (I): 
wherein
R1 and R2 independently represent a group selected from:
(i) C3-8cycloalkyl-;
(ii) hydrogen;
(iii) aryl2CHCH2xe2x80x94;
(iv) C3-8cycloalkylC1-6alkyl-;
(v) C1-8alkyl-;
(vi) arylC1-6alkyl-;
(vii) R4R5Nxe2x80x94C1-6alkyl-;
(viii) C1-6alkyl-CH(CH2OH)xe2x80x94;
(ix) arylC1-5alkyl-CH(CH2OH)xe2x80x94;
(x) arylC1-5alkyl-C(CH2OH)2xe2x80x94;
(xi) C3-8cycloalkyl independently substituted by one or more (e.g. 1, 2 or 3) xe2x80x94(CH2)pR6 groups;
(xii) H2NC(xe2x95x90NH)NHC1-6alkyl-;
(xiii) a group of formula 
xe2x80x83or such a group in which one methylene carbon atom adjacent to X, or both if such exist, is substituted by methyl;
(xiv) xe2x80x94C1-6alkyl-OH;
(xv) xe2x80x94C1-8haloalkyl;
(xvi) a group of formula 
(xvii) aryl; and
(xviii) xe2x80x94(CH2)fSO2NHg(C1-4alkyl-)2-g or xe2x80x94(CH2)fSO2NHg(arylC1-4alkyl-)2xe2x80x94g;
R3 represents methyl, ethyl, xe2x80x94CHxe2x95x90CH2, n-propyl, xe2x80x94CH2CHxe2x95x90CH2, xe2x80x94CHxe2x95x90CHCH3, isopropyl, isopropenyl, cyclopropyl, cyclopropenyl, cyclopropylmethyl, cyclopropenylmethyl, cyclobutyl, cyclobutenyl, xe2x80x94(CH2)qhalogen, xe2x80x94(CH2)hY(CH2)iH, xe2x80x94(CH2)hCOOCH3, xe2x80x94(CH2)hOCOCH3, xe2x80x94(CH2)hCON(CH2)mH((CH2)nH), xe2x80x94(CH2)hCO(CH2)oH or xe2x80x94CH2C((CH2)uH)xe2x95x90NO(CH2)vH;
Y represents O, S or N(CH2)j;
a and b independently represent an integer 0 to 4 provided that a+b is in the range 3 to 5;
c, d and e independently represent an integer 0 to 3 provided that c+d+e is in the range 2 to 3;
f represents 2 or 3 and g represents an integer 0 to 2;
p represents 0 or 1;
q represents 2 or 3;
h represents 2 or 3;
i represents an integer 0 to 2 such that h+i is in the range 2 to 4
j represents an integer 0 to 2 such that h+i+j is in the range 2 to 4
m and n independently represent an integer 0 to 2 such that m+n is in the range 0 to 2;
o represents an integer 0 to 2 such that h+o is in the range 2 to 3;
u and v independently represent 0 or 1 such that u+v is in the range 0 to 1;
R4 and R5 independently represent hydrogen, C1-6alkyl, aryl, arylC1-6alkyl- or NR4R5 together may represent pyrrolidinyl, piperidinyl, morpholinyl, azetidinyl, azepinyl, piperazinyl or Nxe2x80x94C1-6alkylpiperazinyl.
R6 represents OH, NH2, NHCOCH3 or halogen;
R7 represents hydrogen, C1-6alkyl, C1-6alkylaryl or xe2x80x94COC1-6alkyl;
X represents NR7, O, S, SO or SO2;
provided that when R3 represents methyl, ethyl or isopropyl then R1 and/or R2 independently must represent:
(a) xe2x80x94(CH2)fSO2NHg(C1-4alkyl-)2-g or xe2x80x94(CH2)fSO2NHg(arylC1-4alkyl-)2-g where f is 2 or 3 and g is an integer 0 to 2;
(b) C3-8cycloalkyl independently substituted by one or more xe2x80x94(CH2)pNHCOCH3 groups;
(c) a group of formula 
xe2x80x83or such a group in which one methylene carbon atom adjacent to X, or both if such exist, is substituted by methyl;
(d) a group of formula 
and salts and solvates thereof.
References to C1-6alkyl include references to an aliphatic hydrocarbon grouping containing 1 to 6 carbon atoms which may be straight chain or branched and may be saturated or unsaturated although will be preferably saturated. References to C1-4alkyl, C1-5alkyl, C2-4alkyl and C1-8alkyl may be interpreted similarly.
References to aryl include references to mono- and bicyclic carbocyclic aromatic rings (e.g. phenyl, naphthyl) and heterocyclic aromatic rings containing 1-3 hetero atoms selected from N, O and S (e.g. pyridinyl, pyrimidinyl, thiophenyl, imidazolyl, quinolinyl, furanyl, pyrrolyl, oxazolyl) all of which may be optionally substituted, e.g. by C1-6alkyl, halogen, hydroxy, nitro, C1-6alkoxy, cyano, amino, SO2NH2or xe2x80x94CH2OH.
Examples of C3-8cycloalkyl for R1 and R2 include monocyclic alkyl groups (e.g. cyclopentyl, cyclohexyl) and bicyclic alkyl groups (e.g. norbornyl such as exo-norborn-2-yl).
Examples of (aryl)2CHCH2xe2x80x94 for R1 and R2 include Ph2CHCH2xe2x80x94 or such a group in which one or both phenyl moieties is substituted, e.g. by halogen or C1-4alkyl. Examples of C3-8cycloalkylC1-6alkyl- for R1 and R2 include ethylcyclohexyl. Examples of C1-8-alkyl for R1 and R2 include xe2x80x94(CH2)2C(Me)3, xe2x80x94CH(Et)2 and CH2xe2x95x90C(Me)CH2CH2xe2x80x94.
Examples of arylC1-6alkyl- for R1 and R2 include xe2x80x94(CH2)2Ph, xe2x80x94CH2Ph or either in which Ph is substituted (one or more times) by halogen (e.g. iodine), amino, methoxy, hydroxy, xe2x80x94CH2OH or SO2NH2; xe2x80x94(CH2)2 pyridinyl (e.g. xe2x80x94(CH2)2pyridin-2-yl) optionally substituted by amino; (CH2)2imidazolyl or this group in which imidazolyl is N-substituted by C1-6alkyl (especially methyl).
Examples of R4R5Nxe2x80x94C1-6alkyl- for R1 and R2 include ethyl-piperidin-1-yl, ethyl-pyrrolidin-1-yl, ethyl-morpholin-1-yl, xe2x80x94(CH2)2NH(pyridin-2-yl) and xe2x80x94(CH2)2NH2. Examples of C1-6alkyl-CH(CH2OH)xe2x80x94 for R1 and R2 include Me2CHCH(CH2OH)xe2x80x94. Examples of arylC1-5alkyl-CH(CH2OH)xe2x80x94 for R1 and R2 include PhCH2CH(CH2OH)xe2x80x94 especially 
Examples of aryl C1-5alkyl-C(CH2OH)2xe2x80x94 for R1 and R2 include PhCH2C(CH2OH)2xe2x80x94. Examples of C3-8 cycloalkyl independently substituted by one or more xe2x80x94(CH2)pR6 groups (eg 1, 2 or 3 such groups) for R1 and R2 include 2-hydroxy-cyclopentyl and 4-aminocyclohexyl (especially trans-4-amino-cyclohexyl).
Examples of H2NC(xe2x95x90NH)NHC1-6alkyl for R1 and R2 include H2NC(xe2x95x90NH)NH(CH2)2xe2x80x94.
Examples of groups of formula 
for R1 and R2 include pyrrolidin-3-yl, piperidin-3-yl, piperidin-4-yl or a derivative in which the ring nitrogen is substituted by C1-6alkyl (e.g. methyl) or benzyl, tetrahydro-1,1-dioxide thiophen-3-yl, tetrahydropyran-4-yl, tetrahydrothiopyran-4-yl and 1,1-dioxo-hexahydro-1.lamda.6-thiopyran-4-yl.
Examples of xe2x80x94C1-6alkyl-OH groups for R1 and R2 include xe2x80x94CH2CH2OH.
Examples of C1-8haloalkyl for R1 and R2 include xe2x80x94CH2CH2Cl and (CH3)2ClC(CH2)3xe2x80x94.
Examples of groups of formula 
for R1 and R2 include 2-oxo-pyrrolidin-4-yl, 2-oxo-pyrrolidin-5-yl or a derivative in which the ring nitrogen is substituted by C1-6alkyl (e.g. methyl) or benzyl.
Examples of aryl for R1 and R2 include phenyl optionally substituted by halogen (e.g. fluorine, especially 4-fluorine).
Examples of C1-6alkyl for R7 include methyl and C1-6alkylaryl for R7 include benzyl. Examples of COC1-6 alkyl for R7 include xe2x80x94COCH3.
Examples of C1-5alkyl for R3 include n-propyl and allyl. An example of C3-4 cycloalkyl for R3 includes cyclobutyl. An example of xe2x80x94(CH2)hO(CH2)iH for R3 includes xe2x80x94(CH2)2OMe. Examples of C2-4alkyl substituted by halogen or hydroxy include xe2x80x94(CH2)2Cl, xe2x80x94(CH2)2OH and xe2x80x94(CH2)3OH.
We prefer that R1 and R2 do not both represent hydrogen.
We prefer R1 to represent aryl2CHCH2xe2x80x94, C1-8alkyl, hydrogen or aryl C1-6alkyl-.
We particularly prefer R1 to represent Ph2CHCH2xe2x80x94, xe2x80x94CH(Et)2, hydrogen or phenylethyl-, especially Ph2CHCH2xe2x80x94.
We prefer R2to represent R4R5Nxe2x80x94C1-6alkyl-, arylC1-6alkyl-, arylC1-5alkylCH(CH2OH)xe2x80x94, aryl C1-6 alkyl or C1-6 alkyl-CH(CH2OH)xe2x80x94.
We particularly prefer R2 to represent (CH2)2(piperidin-1-yl), 2-(1-methyl-1H-imidazol-4yl)ethyl, 1S-hydroxymethyl-2-phenylethyl, phenylethyl or 1S-hydroxymethyl-2-methyl propyl, especially xe2x80x94(CH2)2(piperidin-1-yl).
We prefer R3 to represent C1-3alkyl (including n-propyl and 2-propenyl), cyclobutyl, cyclopropylmethyl, xe2x80x94(CH2)2OCOCH3, xe2x80x94(CH2)2-3OH or xe2x80x94(CH2)2halogen. More preferably R3 represents n-propyl, 2-propenyl, cyclobutyl, cyclopropylmethyl, xe2x80x94(CH2)2OCOCH3, or xe2x80x94(CH2)2-3OH.
We particularly prefer R3 to represent xe2x80x94(CH2)2OCOCH3, xe2x80x94(CH2)2OH or (CH2)3OH, especially xe2x80x94(CH2)2OCOCH3 or xe2x80x94(CH2)2OH, most especially xe2x80x94(CH2)2OH.
We prefer R4 and R5 independently to represent hydrogen, C1-6alkyl or aryl or NR4R5 together to represent pyrrolidinyl, piperidinyl, morpholinyl, azetidinyl, azepinyl, piperazinyl or N-methylpiperazinyl;
We prefer X to represent NR7, O, S or SO2, particularly NR7 or SO2, especially NR7.
We prefer that a and b both represent 2 or that a represents 1 and b represents 2.
We prefer that R7 represents hydrogen.
We prefer that p represents 0. We prefer q to represent 2. We prefer h to represent 2. We prefer i to represent 0 or 1, especially 0. We prefer j to represent 1. We prefer m and n to represent 0 or 1. We prefer o to represent 1.
We prefer u and v to represent 0.
We prefer that R6 represents OH or NH2 especially NH2.
We prefer that c represents 0 and either d represents 2 and e represents 0 or d represents 1 and e represents 1.
The representation of formula (I) indicates the absolute stereochemistry at positions around the tetrahydrofuran ring. When sidechains contain chiral centres the invention extends to mixtures of enantiomers (including racemic mixtures) and diastereoisomers as well as to individual enantiomers. Generally it is preferred to use a compound of formula (I) in the form of a purified single enantiomer.
We also provide a process for preparation of compounds of formula (I) which comprises:
(a) reacting a corresponding compound of formula (II) 
wherein L represents a leaving group or a protected derivative thereof with a compound of formula R2NH2 or a protected derivative thereof;
(b) preparing a compound of formula (I) in which R1 represents hydrogen by reducing a compound of formula (III) 
xe2x80x83or a protected derivative thereof; or
(c) deprotecting a compound of formula (I) which is protected; and where desired or necessary converting a compound of formula (I) or a salt thereof into another salt thereof.
In process (a) L represents a leaving group such as halogen eg chlorine or fluorine. The reaction of process (a) will generally be carried out on heating the reagents to a temperature of 50xc2x0 C.-150xc2x0 C. in the presence of a solvent such as DMSO. Preferably an organic base, e.g. a trisubstituted organic amine (such as diisopropylethylamine) is also present for the reaction. Under these conditions we particularly prefer that Hal represents fluorine (especially when R1 represents hydrogen) since the reaction has a tendency to proceed rapidly with high efficiency.
In process (b) the reduction reaction may be performed by catalytic hydrogenation, e.g. over Pd/C under standard conditions.
In process (c) examples of protecting groups and the means for their removal can be found in T W Greene xe2x80x9cProtective Groups in Organic Synthesisxe2x80x9d (J Wiley and Sons, 1991). Suitable hydroxyl protecting groups include alkyl (e.g. methyl), acetal (e.g. acetonide) and acyl (e.g. acetyl or benzoyl) which may be removed by hydrolysis, and arylalkyl (e.g. benzyl) which may be removed by catalytic hydrogenolysis. Suitable amine protecting groups include sulphonyl (e.g. tosyl), acyl e.g. benzyloxycarbonyl or t-butoxycarbonyl) and arylalkyl (e.g. benzyl) which may be removed by hydrolysis or hydrogenolysis as appropriate.
Suitable salts of the compounds of formula (I) include physiologically acceptable salts such as acid addition salts derived from inorganic or organic acids, for example hydrochlorides, hydrobromides, 1-hydroxy-2-naphthoates, mesylates, sulphates, phosphates, acetates, benzoates, citrates, succinates, lactates, tartrates, fumarates and maleates, and if appropriate, inorganic base salts such as alkali metal salts, for example sodium salts. Other salts of the compounds of formula (I) include salts which may not be physiologically acceptable but may be useful in the preparation of compounds of formula (I) and physiologically acceptable salts thereof. Examples of such salts include trifluoroacetates and formates.
Examples of suitable solvates of the compounds of formula (I) include hydrates.
Acid-addition salts of compounds of formula (I) may be obtained by treating a free-base of formula (I) with an appropriate acid.
The compounds of formula (II) or a protected derivative thereof may be prepared by reacting a compound of IV 
or a protected derivative thereof with a compound of formula R1NH2. L1 and L2 independently represent a leaving group such as halogen eg chlorine or fluorine. This reaction will preferably be performed in the presence of a base such as an organic amine base (e.g. diisopropyl ethylamine) in a solvate such as an alcohol (e.g. isopropanol) at elevated temperature (e.g. reflux).
Compounds of formula (III) or a protected derivative thereof may be prepared by reacting a compound of formula (IIIA) 
wherein L represents a leaving group such as halogen eg chlorine or fluorine, or a protected derivative thereof, with a compound of formula R2NH2 under conventional conditions.
Compounds of formula (IIIA), or a protected derivative thereof, may be prepared by reacting a compound of formula (IV), or a protected derivative thereof, with an azide, e.g. sodium azide under conventional conditions.
The compound of formula (IV) or a protective derivative thereof may be prepared by reacting a compound of formula (V) 
wherein L represents a leaving group or a protected derivative thereof with a 2,6,dihalopurine, e.g. 2,6-dichloropurine.
We prefer to use the compound of formula (V) wherein the ribose 2- and 3-hydroxyl groups are protected, e.g. by acetyl. Leaving group L may represent OH but will preferably represent C1-6alkoxy (e.g. methoxy or ethoxy), an ester moiety (e.g. acetyloxy or benzoyloxy) or halogen. The preferred group L is acetyloxy. The reaction may be performed by combining the reactants in an inert solvent such as MeCN in the presence of a Lewis Acid (eg TMSOTf) and DBU and warming to, say, 70-80xc2x0 C.
Compounds of formula (V) may be prepared from a compound of formula (VI) 
wherein alk represents C1-6 alkyl eg methyl by treating the compound of formula (VI) with trifluoroacetic acid in water followed by reprotection, e.g. by reaction with acetic anhydride in pyridine.
Compounds of formula (V) in which L represents halogen, may be prepared from the corresponding 1xe2x80x2-alcohol or a 1xe2x80x2-ester such as the acetate. Reaction will generally occur on treatment with anhydrous HCl or HBr. 1xe2x80x2-iodides may be prepared directly on treatment with trimethylsilyliodide and 1xe2x80x2-fluorides may be prepared on treatment with DAST. An inert solvent eg diethylether, DCM, THF or CCI4will generally be suitable.
Compound of formula (VI) may be prepared following Scheme 1: 
General conditions for Stages 1-6 will be known to persons skilled in the art. It will also be appreciated that the reagents and conditions set out in Scheme 1 are example conditions and alternative reagents and conditions for achieving the same chemical transformation may be known to persons skilled in the art. For example an alternative alcohol, e.g. a C1-6alkyl alcohol may be used in Stage 1 to give a different C1-6 alkyloxy leaving group in compounds of formula (VII) and (VI). Stage 1 may also be modified in that the use of HCl can be substituted by perchloric acid (HClO4) and 2,2 dimethoxypropane, or alternatively acetyl chloride (which has the advantage that it maintains high yield and avoids use of perchlorate salts). Alternative reaction conditions can be used in Stage 3, which may utilise ethyl acetate, thionyl chloride and gaseous ammonia (which has the advantage that it avoids chlorinated solvent and the synthesis of troublesome ammonium pivaloate impurity). Stage 4 may also be performed using POCl3, TEA, DMF and ethyl acetate in the reaction conditions (which avoids the use of hazardous DMAP). Compounds of formula (VII) wherein a leaving group besides OMe is desired may be prepared by analogy with the method described above for preparation of compounds of formula (V). Alternative groups may be used to protect the 2xe2x80x2 and 3xe2x80x2 hydroxy groups on the ribose in Stage 1. We have also found that Stage 5 may desirably be performed using azidotrimethylsilane and dibutyltin oxide in toluene.
Following stage 6, the impure product may be purified using conventional techniques, and especially using flash chromatography conditions under nitrogen pressure. We have found that satisfactory conditions include loading the impure product in a minimum volume of dichloromethane onto a Keiselgel 60 (Merck 9385) column and eluting using a gradient solvent system with ethyl acetate (10-40%) in cyclohexane.
Compounds of formula (II), and protected derivatives thereof, may also be prepared by reacting a compound of formula (V), or a protected derivative thereof with a compound of formula (VIII) 
wherein L represents a leaving group such as halogen, e.g. chlorine or fluorine optionally followed by a deprotection or deprotection and reprotection reaction.
We prefer to use compounds of formula (V) in protected form. In particular we prefer that at least the hydroxy group in the 2-position on the ribose is protected as an ester group, e.g. by acetyl or benzoyl since this has a tendency to result in greater stereoselectivity in the coupling reaction. We prefer that the 2- and 3-position hydroxy groups are protected by acetyl. Suitable leaving groups L are a described previously. The preferred leaving group L is acetyloxy.
This process is particularly preferred when L represents fluorine (and most especially when R1 represents hydrogen) since the reaction is generally fast and efficient and the reaction has a tendency to produce products of high crystallinity.
The product of this reaction may be deprotected if desired under conventional conditions eg on treatment with an alcohol (eg isopropanol) under mild basic conditions (eg in the presence of potassium carbonate).
The reaction of compounds of formula (V) (in protected form) and compounds of formula (VIII) may be performed in the presence of a Lewis Acid (eg TMSOTf) and optionally a silylating agent (eg BSA) in an inert solvent such as acetonitrile followed by work-up eg with water. When L represents halogen the Lewis Acid can generally be omitted when a silylating agent is present.
Certain compounds of formula (VIII) are known. Other compounds of formula (VIII) may be prepared by reaction of a compound of formula (IX) 
wherein L1 and L2 independently represent a leaving group such as halogen, e.g. chlorine or fluorine,
with R1NH2 under conventional conditions.
Compounds of formula R1NH2, R2NH2 and IX are either known or may be prepared by conventional methods known per se.
As a further aspect of the invention we also provide new process which may be used to provide compounds of formula (I) without the proviso.
Thus we provide a process for preparation of a compound of formula (I) without the proviso which comprises
(d) reacting a corresponding compound of formula (X) 
xe2x80x83with a compound of formula (XI)
R3xe2x80x94Lxe2x80x83xe2x80x83(XI)
wherein L is a leaving group; or
(e) reacting a corresponding compound of formula (XII) 
xe2x80x83with a compound of formula (V) or a protected derivative thereof.
Process (d) will generally take place on combining the two reagents in the presence of a mild base e.g. K2CO3 and an inert organic solvent eg DMF. Typical leaving groups L include halogen (e.g. Br).
Process (e) will generally take place in the presence of a Lewis Acid (e.g. TMSOTf) and optionally a silylating agent (e.g. BSA) in an inert solvent such as MeCN followed by work-up e.g. with water. We prefer L to represent acetyloxy and the two hydroxy groups to be protected as the acetyl ester. A deprotection step (using mild base e.g. K2CO3) will then be necessary to generate the compound of formula (I).
Compounds of formula (X) may be prepared by analogous methods to those described above for the preparation of compounds of formula (I). When compounds of formula (X) are prepared via the analogues of compounds of formula (II), (III), (IIIA) and/or (IV) in which R3 is replaced by hydrogen, such compounds are preferably protected in the N2-position of the tetrazole. A suitable protecting group is benzyl which may be incorporated by treating the unprotected tetrazole with a benzyl halide (e.g. benzyl bromide) in the presence of base (e.g. K2CO3). An illustrative process for the preparation of compounds of formula (X) is given in Scheme 2: 
Compounds of formula (XI) are known or may be prepared by known methods.
Compounds of formula (XII) may be prepared, for example following Scheme 3: 
Processes (d) and (e) are particularly suitable for preparing the compound (2R,3R,4S,5R)-2-[6-Amino-2-(1S-hydroxymethyl-2-phenyl-ethylamino)-purin-9-yl]-5-(2-ethyl-2H-tetrazol-5-yl)-tetrahydro-furan-3,4-diol and salts and solvates thereof, especially the maleate salt.
We prefer process (e).
The potential for compounds of formula (I) to inhibit leukocyte function may be demonstrated, for example, by their ability to inhibit superoxide (O2xe2x80x94) generation from neutrophils stimulated with chemoattractants such as N-formylmethionyl-leucyl-phenylalanine (fMLP). Accordingly, compounds of formula (I) are of potential therapeutic benefit in providing protection from leukocyte-induced tissue damage in diseases where leukocytes are implicated at the site of inflammation.
Examples of disease states in which the compounds of the invention have potentially beneficial anti-inflammatory effects include diseases of the respiratory tract such as adult respiratory distress syndrome. (ARDS), bronchitis (including chronic bronchitis), cystic fibrosis, asthma (including allergen-induced asthmatic reactions), chronic obstructive pulmonary disease (COPD), emphysema, rhinitis and septic shock. Other relevant disease states include diseases of the gastrointestinal tract such as intestinal inflammatory diseases including inflammatory bowel disease (e.g. Crohn""s disease or ulcerative colitis), Helicobacter-pylori induced gastritis and intestinal inflammatory diseases secondary to radiation exposure or allergen exposure, and non-steroidal anti-inflammatory drug-induced gastropathy. Furthermore, compounds of the invention may be used to treat skin diseases such as psoriasis, allergic dermatitis and hypersensitivity reactions and diseases of the central nervous system which have an inflammatory component eg Alzheimer""s disease and multiple sclerosis.
Further examples of disease states in which compounds of the invention have potentially beneficial effects include cardiac conditions such as peripheral vascular disease, post-ischaemic reperfusion injury and idiopathic hypereosinophilic syndrome.
Compounds of the invention which inhibit lymphocyte function may be useful as immunosuppressive agents and so have use in the treatment of auto-immune diseases such as rheumatoid arthritis and diabetes.
Compounds of the invention may also be useful in inhibiting metastasis.
Diseases of principal interest include asthma and COPD.
It will be appreciated by those skilled in the art that reference herein to treatment extends to prophylaxis as well as the treatment of established conditions.
As mentioned above, compounds of formula (I) are useful in human or veterinary medicine, in particular as anti-inflammatory agents.
There is thus provided as a further aspect of the invention a compound of formula (I) or a physiologically acceptable salt or solvate thereof for use in human or veterinary medicine, particularly in the treatment of patients with inflammatory conditions who are susceptible to leukocyte-induced tissue damage.
According to another aspect of the invention, there is provided the use of a compound of formula (I) or a physiologically acceptable salt or solvate thereof for the manufacture of a medicament for the treatment of patients with inflammatory conditions who are susceptible to leukocyte-induced tissue damage.
In a further or alternative aspect there is provided a method for the treatment of a human or animal subject with an inflammatory condition who is susceptible to leukocyte-induced tissue damage, which method comprises administering to said human or animal subject an effective amount of a compound of formula (I) or a physiologically acceptable salt or solvate thereof.
The compounds according to the invention may be formulated for administration in any convenient way, and the invention therefore also includes within its scope pharmaceutical compositions for use in anti-inflammatory therapy, comprising a compound of formula (I) or a physiologically acceptable salt or solvate thereof together, if desirable, with one or more physiologically acceptable diluents or carriers.
There is also provided a process for preparing such a pharmaceutical formulation which comprises mixing the ingredients.
The compounds according to the invention may, for example, be formulated for oral, buccal, parenteral, topical or rectal administration, preferably for parenteral or topical (e.g. by aerosol) administration.
Tablets and capsules for oral administration may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, mucilage of starch, cellulose or polyvinyl pyrrolidone; fillers, for example, lactose, microcrystalline cellulose, sugar, maize-starch, calcium phosphate or sorbitol; lubricants, for example, magnesium stearate, stearic acid, talc, polyethylene glycol or silica; disintegrants, for example, potato starch, croscarmellose sodium or sodium starch glycollate; or wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in the art. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, for example, sorbitol syrup, methyl cellulose, glucose/sugar syrup, gelatin, hydroxymethyl cellulose, carboxymethyl cellulose, aluminium stearate gel or hydrogenated edible fats; emulsifying agents, for example, lecithin, sorbitan mono-oleate or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, fractionated coconut oil, oily esters, propylene glycol or ethyl alcohol; or preservatives, for example, methyl or propyl p-hydroxybenzoates or sorbic acid. The preparations may also contain buffer salts, flavouring, colouring and/or sweetening agents (e.g. mannitol) as appropriate.
For buccal administration the compositions may take the form of tablets or lozenges formulated in conventional manner.
The compounds may also be formulated as suppositories, e.g. containing conventional suppository bases such as cocoa butter or other glycerides.
The compounds according to the invention may also be formulated for parenteral administration by bolus injection or continuous infusion and may be presented in unit dose form, for instance as ampoules, vials, small volume infusions or pre-filled syringes, or in multi-dose containers with an added preservative. The compositions may take such forms as solutions, suspensions, or emulsions in aqueous or non-aqueous vehicles, and may contain formulatory agents such as anti-oxidants, buffers, antimicrobial agents and/or tonicity adjusting agents. Alternatively, the active ingredient may be in powder form for constitution with a suitable vehicle, e.g. sterile, pyrogen-free water, before use. The dry solid presentation may be prepared by filling a sterile powder aseptically into individual sterile containers or by filling a sterile solution aseptically into each container and freeze-drying.
By topical administration as used herein, we include administration by insufflation and inhalation. Examples of various types of preparation for topical administration include ointments, creams, lotions, powders, pessaries, sprays, aerosols, capsules or cartridges for use in an inhaler or insufflator, solutions for nebulisation or drops (e.g. eye or nose drops).
Ointments and creams may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or gelling agents and/or solvents. Such bases may thus, for example, include water and/or an oil such as liquid paraffin or a vegetable oil such as arachis oil or castor oil or a solvent such as a polyethylene glycol. Thickening agents which may be used include soft paraffin, aluminium stearate, cetostearyl alcohol, polyethylene glycols, microcrystalline wax and beeswax.
Lotions may be formulated with an aqueous or oily base and will in general also contain one or more emulsifying agents, stabilising agents, dispersing agents, suspending agents or thickening agents.
Powders for external application may be formed with the aid of any suitable powder base, for example, talc, lactose or starch. Drops may be formulated with an aqueous or non-aqueous base also comprising one or more dispersing agents, solubilising agents or suspending agents.
Spray compositions may be formulated, for example, as aqueous solutions or suspensions or as aerosols delivered from pressurised packs, with the use of a suitable propellant, e.g. dichlorodifluoromethane, trichlorofluoromethane, dichlorotetra-fluoroethane, 1,1,1,2,3,3,3-heptafluoropropane, 1,1,1,2-tetrafluoroethane, carbon dioxide or other suitable gas.
Intranasal sprays may be formulated with aqueous or non-aqueous vehicles with the addition of agents such as thickening agents, buffer salts or acid or alkali to adjust the pH, isotonicity adjusting agents or anti-oxidants.
Capsules and cartridges of for example gelatin, or blisters of for example laminated aluminium foil, for use in an inhaler or insufflator may be formulated containing a powder mix of a compound of the invention and a suitable powder base such as lactose or starch.
Solutions for inhalation by nebulation may be formulated with an aqueous vehicle with the addition of agents such as acid or alkali, buffer salts, isotonicity adjusting agents or antimicrobials. They may be sterilised by filtration or heating in an autoclave, or presented as a non-sterile product.
The pharmaceutical compositions according to the invention may also be used in combination with other therapeutic agents, for example anti-inflammatory agents (such as corticosteroids (eg fluticasone propionate, beclomethasone dipropionate, mometasone furoate, triamcinolone acetonide or budesonide) or NSAIDs (eg sodium cromoglycate)) or beta adrenergic agents (such as salmeterol, salbutamol, formoterol, fenoterol or terbutaline and salts thereof) or antiinfective agents (eg antibiotics, antivirals).
The invention thus provides, in a further aspect, a combination comprising a compound of formula (I) or a physiologically acceptable salt or solvate thereof together with another therapeutically active agent, for example an anti-inflammatory agent such as a corticosteroid or NSAID.
The combination referred to above may conveniently be presented for use in the form of a pharmaceutical formulation and thus pharmaceutical formulations comprising a combination as defined above together with a physiologically acceptable diluent or carrier thereof represent a further aspect of the invention.
The individual components of such combinations may be administered either sequentially or simultaneously in separate or combined pharmaceutical formulations. Appropriate doses of known therapeutic agents will be readily appreciated by those skilled in the art.
Compounds of the invention may conveniently be administered in amounts of, for example, 0.01 to 500 mg/kg body weight, preferably 0.01 to 100 mg/kg body weight, 1 to 4 times daily. The precise dose will of course depend on the age and condition of the patient and the particular route of administration chosen.
The compounds of the invention have the advantage that they may be more efficacious, show greater selectivity, have fewer side effects, have a longer duration of action, be more bioavailable by the preferred route, show less systemic activity when administered by inhalation or have other more desirable properties than similar known compounds.
In particular the compounds of the invention have the advantage that they may show greater selectivity for the adenosine 2a receptor subtype over other adenosine receptor subtypes (especially the A1 and A3 receptor subtypes) than hitherto known compounds.
As a further aspect of the invention we provide certain compounds as new and useful intermediates.
Compounds of the invention may be tested for in vitro and in vivo biological activity in accordance with the following screens:
(1) Agonist activity against adenosine 2a, adenosine 1 and adenosine 3 receptor subtypes.
Agonist selectivity of compounds against other human adenosine receptors is determined using Chinese hamster ovary (CHO) cells transfected with the gene for the relevant human adenosine receptor following a method based on that of Castanon and Spevak, 1994. The CHO cells are also transfected with cyclic AMP response elements promoting the gene for secreted placental alkaline phosphatase (SPAP) (Wood, 1995). The effect of test compounds is determined by their effects on basal levels of cAMP (A2a ) or on forskolin-enhanced cAMP (A1 and A3) as reflected by changes in levels of SPAP. EC50 values for compounds are then determined as a ratio to that of the non-selective agonist N-ethyl carboxamide adenosine (NECA).
(2) Antigen-induced lung eosinophil accumulation in sensitised guinea pigs.
Ovalbumin sensitised guinea pigs are dosed with mepyramine (1 mg/kg ip) to protect against anaphylactic bronchospasm. A compound of the invention is then given by the inhaled route (30 min breathing of an aerosol of the compound) immediately prior to ovalbumin challenge (30 min breathing of an aerosol generated from a 50 ug/ml solution of ovalbumin). Twenty four hours after challenge, the guinea pigs are killed and the lungs lavaged. Total and differential leukocyte counts are then obtained for the bronchoalveolar lavage fluid and the dose of test compound giving a 50% reduction in eosinophil accumulation (ED50) is determined (Sanjar et al. 1992).
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